Wikia

Pseudo-historical stories are stories which are set in Earth's past, relative to the date of publication or broadcast. Like The Book of Kells or The Unicorn and the Wasp, they

are wholly or predominantly set in the past, and
have a significant science fiction or science fantasy element aside from the presence of the Doctor and his TARDIS

Note the importance of the first point. Pseudo-historical stories are dominantly set in the past, relative to the date of publication or broadcast. Many Doctor Who stories have brief instances of time travel in to the past, like Timelash or Silver Nemesis, but these "side trips" do not make the story as a whole a pseudo-historical.

Contrast with Doctor Who historical stories, like The Marian Conspiracy or The Aztecs, which are often of an educational nature, with no science fiction element added in. These are frequently, if probably erroneously, called "pure historicals", and they have their own category.